include ../_util-fns :marked Angular 2 applications are styled with regular CSS. That means we can apply everything we know about CSS stylesheets, selectors, rules, and media queries to our Angular applications directly. On top of this, Angular has the ability to bundle *component styles* with our components enabling a more modular design than regular stylesheets. In this chapter we learn how to load and apply these *component styles*. # Table Of Contents * [Using Component Styles](#using-component-styles) * [Special selectors](#special-selectors) * [Loading Styles into Components](#loading-style) * [Controlling View Encapsulation: Emulated, Native, and None](#controlling-view-encapsulation-native-emulated-and-none) * [Appendix 1: Inspecting the generated runtime component styles](#inspect-generated-css) * [Appendix 2: Loading Styles with Relative URLs](#relative-urls) **[Run the live code](/resources/live-examples/component-styles/ts/plnkr.html) shown in this chapter.** .l-main-section :marked ## Using Component Styles For every Angular 2 component we write, we may define not only an HTML template, but also the CSS styles that go with that template, specifying any selectors, rules, and media queries that we need. One way to do this is to set the `styles` property in the component metadata. The `styles` property takes an array of strings that contain CSS code. Usually we give it one string as in this example: +makeExample('component-styles/ts/app/hero-app.component.ts')(format='.') :marked Component styles differ from traditional, global styles in a couple of ways. Firstly, the selectors we put into a component's styles *only apply withing the template of that component*. The `h1 { }` selector in the example above only applies to the `

` tag in the template of `HeroAppComponent`. Any `

` elements elsewhere in the application are unaffected. This is a big improvement in modularity compared to how CSS traditionally works: 1. We can use the CSS class names and selectors that make the most sense in the context of each component. 1. Class names and selectors are local to the component and won't collide with classes and selectors used elsewhere in the application. 1. Our component's styles cannot be changed by changes to styles elsewhere in the application. 1. We can co-locate the CSS code of each component with the TypeScript and HTML code of the component, which leads to a neat and tidy project structure. 1. We can change or remove component CSS code in the future without trawling through the whole application to see where else it may have been used. We just look at the component we're in. a(id="special-selectors") .l-main-section :marked ## Special selectors Component styles have a few special selectors from the world of shadow DOM style scoping. ### :host Use the `:host` pseudo-class selector to target styles in the element that hosts the component (as opposed to targeting elements inside the component's template): +makeExample('component-styles/ts/app/hero-details.component.css', 'host')(format='.') :marked This is the only way we can target the host element. We cannot reach it from inside the component with other selectors, because it is not part of the component's own template. It is in a parent component's template. Use the function form to apply host styles conditionally by including another selector inside parentheses after `:host`. In the next example we target the host element again, but only when it also has the `active` CSS class. +makeExample('component-styles/ts/app/hero-details.component.css', 'hostfunction')(format=".") :marked ### :host-context Sometimes it is useful to apply styles based on some condition outside a component's view. For example, there may be a CSS theme class applied to the document `` element, and we want to change how our component looks based on that. Use the `:host-context()` pseudo-class selector. It works just like the function form of `:host()`. It looks for a CSS class in any ancestor of the component host element, all the way up to the document root. It's useful when combined with another selector. In the following example, we apply a `background-color` style to all `

` elements inside the component, only if some ancestor element has the CSS class `theme-light`. +makeExample('component-styles/ts/app/hero-details.component.css', 'hostcontext')(format='.') :marked ### /deep/ Component styles normally apply only to the HTML in the component's own template. We can use the `/deep/` selector to force a style down through the child component tree into all the child component views. The `/deep/` selector works to any depth of nested components, and it applies both to the view children and the content children of the component. In this example, we target all `

` elements, from the host element down through this component to all of its child elements in the DOM: +makeExample('component-styles/ts/app/hero-details.component.css', 'deep')(format=".") :marked The `/deep/` selector also has the alias `>>>`. We can use either of the two interchangeably. .alert.is-important :marked The `/deep/` and `>>>` selectors should only be used with emulated view encapsulation. This is the default and it is what we use most of the time. See the [Controlling View Encapsulation](#controlling-view-encapsulation-native-emulated-and-none) section for more details. a(id='loading-styles') .l-main-section :marked ## Loading Styles into Components We have several ways to add styles to a component: * inline in the template HTML * by setting `styles` or `styleUrls` metadata * with CSS imports The scoping rules outlined above apply to each of these loading patterns. ### Styles in Metadata We can add a `styles` array property to the `@Component` decorator. Each string in the array (usually just one string) defines the css. +makeExample('component-styles/ts/app/hero-app.component.ts') :marked ### Template Inline Styles We can embed styles directly into the HTML template by putting them inside `